Last night I tried the star collimation technique outlined by Mike Lockwood in his website http://www.loptics.c.../starshape.html
The technique is not easy. It took me a while to make "mental" adjustments to use it. Below are the initial issues I ran into:
1- When I defocused to observe the direction of the "bulge/pull" of the expanding star at high magnification, the scope vibrated and I could not detect the expansion direction with good certainty. The little vibration was caused by touching/twisting the focuser knob. The vibration amount is small but it was enough to impact readability.
2- I initially was expanding the defocused star too much. The offset of the secondary shadow was throwing me off.
3- In general, the mental power of suggestion was strong. When I mentally suggested that the bulge is moving to the right, I saw it it moving to the right. In the second attempt, I mentally suggested that the expansion was in the opposite direction and I saw it as such.
The reason I listed the above issues is to convey that Mike's technique will require practice and more practice to master it. After spending around an hour practicing and making steps/mental corrections, I was able to get a good handle on the technique. Here is what I eventually was doing:
1- I started off with a well-collimated scope then placed my paracorr
2- I severely miscollimated the primary mirror using only two knobs
3- I placed a low magnification eyepiece to locate Procyon
4- Using the low magnification eyepiece, I defocused the star outward too much then used only two primary knobs to recenter the dounut shape in the defocused star. This is meant as a coarse collimation to bring collimation closer. Only one of the two knobs was used in the initial miscollimation. The idea is to enforce fairness during re-collimation.
5- I replaced the low magnification eyepiece with highest-powered eyepiece. I took magnification up to 660X. I have an equatorial table. Tracking was not a problem.
6- I used the expansion star technique described by Mike in his website. Few hints:
a) Use the highest magnification eyepiece you have. The technique works better at high magnification. In my case, I used my 2-4mm TV eyepiece set at 2mm.
b) Do not defocus too much
c) Practice to mentally subtract/cancel vibrations. It can be done. I did it. You will need to expand/reset repeatedly while mentally canceling vibrations.
d) Defocus on both direction as Mike mentioned
e) One thing helped me is concentrating on the expansion in the Y direction then again on in the X direction while I repeatedly expanded/reset. Once I got a feel for X and Y amounts, I moved the star in the expansion direction referencing the X/Y relative amounts.
f) Resist looking at the Fresnel rings. Just concentrate on the bulge/pull/expansion direction.
I repeated the above 6 time. Below are the results:
I am pleased with the results. Much better than using the traditional star collimation technique. I guess you could say that Mike Lockwood rewrote the book on star collimation
By no means I have mastered Mike's technique. I need more practice and experience.